What can Ferns tell us about their environment?

Many people think that ferns are delicate and can only survive in moist locations with a continuous water supply, neither too hot nor too frigid. To some extent this is true. Ferns need liquid water during their development from spore to full plant. But once growing in the soil, some ferns are very hardy indeed. And different ferns tolerate different climatic extremes. Some can survive prolonged drought in semi-desert conditions. Other species are adapted to surviving under feet of snow. Yet others thrive in alkaline soil.

The interesting point is that each fern has its own preferences for temperature; humidity; soil type, moisture and pH; light levels etc. In many cases, ferns are very specific indicators of the conditions they need - often more so than the flowering plants.

In areas where the climate does not favour a riot of fern growth - and the Canberra Region is a case in point - the niche environments are very clearly marked by the types of fern that grow there. Ferns in fact provide a remarkably good set of ecological indicators. Here are some examples from around Canberra.

• Asplenium bulbiferum, Mother Spleenwort, grows only near permanent running water, usually in or near waterfalls. The same is true for Hymenophyllum cupressiforme, Filmy Fern.

 
• Asplenium trichomanes, the Common Spleenwort, grows only on or near limestone outcrops. I was able to test this hypothesis when I first heard about it. Max Gray, then head of the Australian Herbarium, mentioned that he had only found A. trichomanes around limestone outcrops. I asked him if he'd looked at the vegetation near a well known dry limestone cave south of Canberra. He hadn't, so the next weekend I went down there to look. Sure enough, A. trichomanes was growing everywhere among the limestone boulders, to the exclusion of any other fern.
Twenty years later, it is still growing in the same location, despite droughts and blackberry infestations.
 
• Pteridium esculentum, Common (Austral) bracken, always grows where there is adequate soil moisture and deep soil, usually in fairly well lit, exposed conditions.

 
• Blechnum penna-marina, Alpine Water Fern, grows in abundance in the sphagnum bogs at the top of the ranges, and is buried under feet of snow during winter. Few other species tolerate such extremes.

The very useful thing about all these ferns is that their occurrence is very reliable in the right conditions. They are an "indicator" of their preferred ecological niche.

In areas where the conditions are more generous to ferns, the species that can grow in the Canberra Region have a much broader range of places they find acceptable to grow, So, in such benign places, these ferns are less good at pin-pointing the niche environments. Then, of course, other, more fussy ferns take on the job of micro-niche indicators.

This association of species with soil and microclimate shows clearly what conditions are needed to grow the ferns in your own garden. In other words, observing ecological niche dwellers provides useful horticultural information.

This brings us to the broader topic of ecology, and the measurement of environment.

Ferns and Ecology

Such studies provide baseline information for further research into the dynamics and distribution of plant species or communities and how they relate to the physical environment.

Site data and vegetation maps provide information for land-use decisions by Government, industry and the general public. The information is used in decision making on habitat conservation and natural resource management.

As ferns are very good indicators of their immediate environment, conducting surveys of fern flora in an area provides a valuable ecological tool to measure environments to the micro level.

This is where fern-seeking can help in studying the ecology of a region. The amateur has a big part to play.